A padlock of the type described is shown in U.S. Pat. No. 3,766,758, issued Oct. 23, 1973, the disclosure of which is hereby incorporated by reference. In this padlock, release of the dials from the sleeves, which make up the tumblers, in order to permit relative rotation therebetween and a change in the combination, is brought about by displacing a shaft on which the tumblers are mounted. Displacement of the shaft is effected by movement of the shackle after the lock has been opened. Specifically, after the correct or open combination has been dialed, the shackle can be pulled outwardly of the lock and rotated 180.degree. about the axis of the long leg of the shackle from a first to a second angular position. Upon reinsertion into the lock body of the long leg in its second angular position, a cam on the internal end of the long leg will be positioned next to an end of the shaft carrying the tumblers. The shackle can then be rotated out of its second angular position causing the cam to engage the end of the shaft and displace it to release the dials from the sleeves. After a new combination has been selected, the shackle can be rotated back to its second angular position, retracted, and then rotated 180.degree. back to its first angular position in preparation for reinsertion to the body. After reinsertion, the tumblers can be scrambled to retain the shackle in the body thereby locking the padlock.
The chief advantages of this arrangement are that the combination can be changed only after the lock is open, thus requiring a person desiring to change the combination to have knowledge of the open or correct combination; that the essential shackle is constructed to enable its use to change or set the combination; and that there is no visible or obtrusive means for changing the combination. There is the disadvantage, however, in that the combination cannot be scrambled when the lock is open. As a consequence, the correct combination is ascertainable by an unauthorized person when the lock is open; also, the combination can be reset surreptitiously by an unauthorized person whenever the lock is open.
It is therefore an object of the present invention to provide a new and improved combination padlock of the type described wherein the limitations outlined above are overcome.